A number of eukaryotic proteins that seem to be involved with sterol synthesis and/or its regulation have been found [1] to be evolutionary related:

• Mammalian oxysterol-binding protein (OSBP). A protein of about 800 amino- acid residues that binds a variety of oxysterols: oxygenated derivatives of cholesterol. OSBP seems to play a complex role in the regulation of sterol metabolism.
• Mammalian OSBP-related proteins 1 to 11.
• Yeast proteins HES1 and KES1; highly related proteins of 434 residues that seem to play a role in ergosterol synthesis.
• Yeast OSH1 to OSH7.

All these proteins contain a moderately conserved domain of about 250 residues located in the C-terminal half of OBSP, OSH1 and YHR073w and in the central section of the other proteins. As a signature pattern, we selected the best conserved part of this domain, a region that contains a conserved pentapeptide.